Hi all,
Currently, producing an Objective-C selector in Swift is an error-prone
operation. One effectively just writes a string literal and uses it in a
context where an ObjectiveC.Selector is expected:
control.sendAction(“doSomething:”, to: target, forEvent: event)
There are many points of failure here:
1) The compiler doesn’t syntax-check at all to make sure it’s a valid spelling
for a selector
2) The compiler doesn’t look for existing methods with this selector anywhere
3) The mapping from a Swift method name to an Objective-C selector isn’t always
immediately obvious (especially for initializers), and will be getting
significantly more complicated with the renaming work for Swift 3
(https://github.com/apple/swift-evolution/blob/master/proposals/0005-objective-c-name-translation.md).
I suggest that we add an expression ‘objc_selector(method-reference)` that
produces the Objective-C selector for the named method, and produces an error
if the method does not have an Objective-C entry point. For example:
control.sendAction(objc_selector(MyApplication.doSomething), to:
target, forEvent: event)
“doSomething” is a method of MyApplication, which might even have a
completely-unrelated name in Objective-C:
extension MyApplication {
@objc(jumpUpAndDown:)
func doSomething(sender: AnyObject?) { … }
}
By naming the Swift method and having objc_selector do the work to form the
Objective-C selector, we free the programming from having to do the naming
translation manually and get static checking that the method exists and is
exposed to Objective-C.
This proposal composes with my “Generalized Naming for Any Function” proposal,
which lets us name methods fully, including getters/setters:
let sel1: Selector = objc_selector(UIView.`insertSubview(_:at:)`) //
produces the Selector “insertSubview:atIndex:"
let sel2: Selector = objc_selector(UIView.`frame.get`) // produces the
Selector “frame"
I don’t like the `objc_selector` syntax at all, but otherwise I think this
functionality is straightforward.
- Doug
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
